Electronic stethoscope



y 1964 D. A. DYMSKI ETAL 3,132,208

ELECTRONIC STETHOSCOPE Filed June 22, 1961 9 Sheets-Sheet 1 IO SENSING DEVICE l2 I5 I 6 i EM'TTER AMPLIFIER GATE FOLLOWER EMITTER EMITTER AMPLIFIER FOLLOWER FOLLOWER I4 5 2s EM'TTER GATE I AMPLIFIER FOLLOWER CONTROL INVENTORS DONALD A. DYMSKI JOSEPH M. SOLOMON BY @140, Mi ATTORNEYS May 5, 1964 D. A. DYMSKI ETAL Filed June 22, 1961 9 Sheets-Sheet 2 ELECTRODES T {Q v 7 IO SENSING DEVICE DIFFERENTIAL AMPLIFIER I2 l8 EM'TTER AMPLIFIER FOLLOWER l3 l9 AMPLIFIER EM'TTER FOLLOWER AMPLIFIER I4 20 EMITTER AMPLIFIER FOLLOWER 25 EMITTER 5 FOLLQWER 2| PUP] R EMITTER AM E 24 FOLLOWER IIANDII I09 l6 GATE 22 EMITTER I oELAY FoLLowER MULTIVIBRATOR GATE MULTIVIBRATOR INVENTORS DONALD A. DYMSKI JOSEPH M. SOLOMON ATTORNEYS y 5, 1964 A. DYMSKI ETAL 3,132,208

ELECTRONIC STETHOSCOPE.

Filed June 22, 1961 9 Sheets-ShetS INVENTORS DONALD A. DYMSKI JOSEPH M. SOLOMON ATTORNEYS y 5, 1964 D. A. DYMSKI ETAL 3,132,208

ELECTRONIC STETHOSCOPE Filed June 22, 1961 -9 Sheets-Sheet 4 OUTPUT E T INVENTORS SENSING DEV|CE-IO DONALD DYMSK' I N JOSEPH M. SOLOMON A TTOR/VEYS May 5, 1964 D. A. DYMSKI ETAL ELECTRONIC STETHOSCOPE 9 Sheets-Sheet 5 Filed June 22, 1961 INVENTORS DONALD A DYMSKI JOSEPH M. SOLOMON AT ORNEYS May 5, 1964 D. A. DYMSKI ETAL 3,132,203

ELECTRONIC STETHOSCOPE Filed June 22, 1961 I 9 Sheets-Sheet 6 "f0 GATE 24 INVENTORS DONALD A. DYMSKI JOSEPH M. SOLOMON A T TORNE' Y5 May 5, 1964 D. A. DYMSKI ETAL ELECTRONIC STETHOSCOPE 9 Sheets-Sheet 7 Filed June 22, 1961 May 5, 1-964 D. A. DYMSKI ETAL ELECTRONIC STETHOSCOPE 9 Sheets-Sheet 8 Filed June 22, 1961 INVENTORS DONALD A DYMSKI JOSEPH M. SOLOMON BY QM, @Q w A 7"TORIVE YS May 5, 1964 D. A. DYMSKI ETAL ELECTRONIC STETHOSCOPE Filed June 22, 1961 9 Sheets-Sheet 9 BY @W. @m,

INVENTORB DONALD A. DYMSKI JOSEPH M. SOLOMON ATTORNEYS the internal sounds United States Patent fofifice 3,132,208 Patented May 5, 1964 3,132,208 ELECTRQN C STETHOSCOPE Donald A. Dymski, Eggertsville, and Joseph M. Solomon, Lockport, N.Y., assignors to Bell Aerospace Corporation, Wheatfield, N.Y.

Filed June 22, 1961, Ser. No. 118,837 3 Claims. (Cl. 179-1) This invention relates to electronic stethoscopes and more particularly to the combination in an electronic systern of such a stethoscope with means to remove undesired sounds so that other sounds can be amplified, studied and/ or recorded without interference from the undesired sounds.

It is a principal object of this invention to provide an improved and simplified system for use in the diagnosis and treatment of bodily conditions, which system not only provides electronic amplification of sounds to increase their strength andthereby facilitate analysis of their significance, but also provides means for eliminating certain sounds without weakening amplification can be used servation of the latter. a

The system will be described with reference to the enhancement of cardiovascular sounds, although its usefulness is by no means limited thereto, and detailed examples, will be discussed hereinafter to show how the present system employs time basis filtering to remove undesired sounds so that other sounds can be amplified, studied and/or recorded without interference from the undesired sounds.

Present-day electronic equipment used in connection with this type of medical analysis is quite complex, bulky, and quite often available only in larger hospitals, such complex equipment generally being restricted to use by specially trained personnel. The present invention is designed to eliminate the need for electronically trained personnel and to allow a physician to use this device directly to obtain first-hand information from audible signals important in connection with diagnoses. Such physician can not only obtain his own information concerning from a patients body, but permanent conveniently recorded and maintained overa period of time so as to make to full advantage during obrecords can also be by such physician these records available if wanted at a later date, for purposes of comparison with the patients condition at such later time. This apparatus also has great utility in the training of medical students.

. The technique of filtering out cardiovascular sounds on a real-time basis is accomplished by the present invention in two different ways. One way consists of utilizing the phonocardiogram signal directly, whereas the other approach uses electrocardiograph signals to control electronic gate means connected to the phonocardiogram signal so as to obliterate unwanted sounds occurring at instants of time bearing a fixed relationship with respect to such electrocardiographic signals.

The specific equipment and techniques involved in performing the aforementioned analyses can be bestillustrated by first describing the spectrum of the heartbeat. The first occurrence is not audible, but comprises an electric signal which can be picked up as a pulse by electrocardiographic circuits. This signal initiates the heart activitywhich comprises two dominant sounds, the first sound occurring with the apex impulse and corresponding with the beginning of the ventricular systole. sound is followed by a second sound which occurs after the systole and marks the beginning of the ventricular diastole. The first sound is generally louder than the second-sound, and is sometimes followed by other sounds indicating heart abnormalities often referred to as murmurs. The murmurs probably are at a still smaller amother sounds so that electronic the louder sounds, such as electronic stethoscope plitude, and may be somewhat overshadowed by the louder ventricular sounds.

It is an important object of this invention not only to provide means for amplifying the various sounds, but also to provide means for selecting and/or filtering out the normal heartbeats comspecific technique employed in selecting only that portion of the spectrum second sound occurring at the beginning of the ventricular diastole will be referred to as the dominant II sound of the heart.

Other objects and advantages of this invention will become apparent during the following discussion of the drawings, wherein:

FIG. 1 is a block diagram of an electronic employing time basis filtering;

FIG. 2 is a block diagram of a system combining an with electrocardiographic equipstethoscope ment to provide a system in which electrical impulses serve to control the filtering of the audible up by the stethoscope microphone;

FIG. 3 is an illustration of a heartbeat signal'illustrating the dominant I and dominant II sounds;

FIG. 4 is similar to FIG. 3 but showing the presence of a heart murmur;

FIG. 5 is an illustration of the signal output of the gate control 5 of FIG. 1 and showing its orientation relasounds picked tive to the signal of FIG. 3 or 4;

FIG. 6 is an illustration of the triggering Waveform dc livered to multivibrator 22 in FIG. 2;

FIG. 7 is an illustration of the signal output of the gate control multivibrator 23 of FIG. 2 and showing its orientation relative to the signal of FIG. 3 or 4; a

FIG. 8 is an. illustration of a representative signal emanating from the gate 6 of FIG. 1 or the gate 24 of FIG. 2;

'FIG-.- 9 is a schematic circuit diagram showing a portion of the stethoscope circuit which is common to both the system of FIG. 1 and the system of FIG. 2;

FIG. 10 is a schematic diagram of a portion of the circuit according to'the system of FIG. 2;

FIG. 11 is a schematic diagram of the gate control means used specifically in the system of FIG. 2;

FIG. 12 is a schematic diagram of the gate and subsequent circuitry used in the system of FIG. 2;

FIG. 13 is a schematic diagram ofthe gate and subsequent circuitry used in the system of FIG. 1; and

FIG. 14 is a schematic diagram of the gate control 5 of FIG. 1.

Referring now both to FIGS. 1 and 2, as shown in each, the heartbeat or other bodily sound is detected by an appropriate sensing device such as a crystal microphone 10 and "is introduced into an emitter-follower circuit 12 which serves as an impedance matching device for match ing the higher impedance of the microphone 10 to the lower impedance of'the following amplification means. Preferably, such amplification means comprises the amplifiers 13 and 15 having an additional emitter-follower at stages mentioned so far is amplification as distinguished from filtering, etc. If the electronic stethoscope were useful merely to increase the amplitude of the detected sounds, it would only be necessary to provide a loud speaker or earphones at the output of the stage 16. The circuitry of the system as thus far described may be used in common with both the systems of FIGS. 1 and 2. According to the system of FIG. 1, a gate circuit 6 18 provided to which the output of the emitter-follower 16 is coupled by way of line 4, and the conductivity of this gate 6 is determined by a control circuit 5. The output of the gate 6, if any, is then delivered to an emitter-follower 25 and an amplifier 26 which in turn comprises the listening device represented in FIG. 1 by earphones 27. Means are provided for rendering the gate control inoperative, as will be discussed hereinafter in greater detail.

Referring to FIG. 2, in contrast to the system of FIG. 1 wherein the gate control 5 is connected to the emitterfollower 16, the gate control of FIG. 2, comprising the delay multivibrator 22 and the gate multivibrator 23, is connected to electrocardiographic equipment. The gate 24 controls the flow of the signal from the microphone 10 and the amplifiers 12, 13, 14, and 16 to a final amplifier 26 which is coupled with the gate 24 by an emitterfollower 25. Finally, the signal from the amplifier 26 is delivered to some sort of audio transducer such as a loud speaker, or headphones 27, or some other device which may provide an audible and/or a visual record. On the right side of FIG. 2, a differential amplifier 17 amplifies the signals picked up by cutaneous electrodes 11, in a manner well known per se, and delivers its signal to a first amplifier stage 18 coupled by an emitter-follower 19 to a second amplifier stage 20 which is in turn coupled with a delay multivibrator 22 by an emitter-follower 21. The delay multivibrator 22 in turn is coupled with a gate control multivibrator 23, the output of which is delivered to the gate 24 and controls the gate to either pass or reject the amplitude sound signals from the microphone 10.

FIG. 9 shows a practical embodiment of a circuit comprising the stages 12, 13, 14, 15 and 16 as well as microphone 10, which may be used in either the system of FIG. 1 or FIG. 2. In FIG. 9, the microphone 10 is coupled with emitter-follower stage 12 including a transister 30 having its collector returned to a source of plus voltage, and having its base coupled for alternating current with the microphone 10 by way of a condenser 31. 'A relatively small capacitor 32 is coupled from the base 5 to ground to shunt any high-frequency noise component signals which might be issued from the microphone. The emitter electrode of the transistor 30 is returned to ground by a resistor 33, and the output from the emitter is connected to the next succeeding stage by a blocking capacitor 34. The emitter-follower stage 12 acts as an impedance-matching device between the microphone 10 and the first amplifier stage 13, which amplifier includes a transistor 35 having its collector coupled to the source of plus voltage through a load resistor 36 and having its emitter returned to ground through a resistance 37 bypassed by a capacitor 38 in a well known manner. The base of the transistor 35 is coupled by the condenser 34 from the emitter-follower stage 12 and a voltage divider chain including resistors 39 and 40 provides forward bias on the base of the transistor 35-to such an extent that the quiescent collector voltage is equal to about one-half of the supply voltage. An additional resistor 41 is coupled from the collector to the base for the purpose of supplying a certain amount of degenerative feedback.

The output from this amplifier stage 13 is coupled to the amplifier stage 15 through another emitter-follower stage 14 including a transistor 42 which serves to isolate the amplifier stage 13 from the amplifier stage 15. The emitter-follower transistor 42 is coupled by a capacitor 43 to the preceding amplifier stage and presents a high impedance load to the collector of that stage, a small capacitor 44 being coupled to ground thereacross in order to further filter out unwanted high frequency components. The collector of the transistor 42, which is, incidentally, of opposite conductivity type as compared with the NPN transistors 30 and 35, is returned to ground. The emitter of the transistor 42 is connected to a source of positive voltage by a load resistor 45, and the output across this resistor 45 is coupled by a capacitor 46 to the base of the next succeeding transistor comprising the amplifier stage 15.

The transistor 47 comprising the amplifier stage 15 has its base coupled to the preceding emitter-follower stage 42 by the capacitor 46 and this base is also bypassed by a small condenser 48 in order to eliminate unwanted high frequency components. Since the transistor 47 is a PNP transistor, its collector electrode is coupled to a minus source of voltage through a load resistor 49, and the emitter of this transistor is returned through two resistances 50 and 51 to ground, the latter resistance being bypassed by a condenser 52 so that the emitter circuit is only partially bypasesd, thereby permitting the unbypassed resistor 50 to provide a certain amount of degenerative feedback in the amplifier transistor 47. A chain of resistors 53 and 54 provide forward bias on the base of the transistor 47 to such an extent that the quiescent collector potential is one-half of the negative supply voltage. Finally, the output from the amplifier transistor 47 passes through an emitter-follower stage 16 including a transistor 55 coupled by a capacitor 56 to the load resistor 49 of the preceding stage, and this emitter-follower is biased somewhat in the forward direction by a chain of resistors 57 and 58. The base of the transistor 55 is again bypassed for high frequency by a small capacitor 59. Since the transistor 55 is an NPN transistor, its collector is returned to a source of positive voltage and its emitter is coupled to ground through an output load reslstance 61). The output from this last emitter-follower stage 16 is taken from the load resistor 60 by a lead 61 which is coupled to the gate circuit 24, as illustrated in FIG. 2.

The signals passing from the emitter-follower 16 are of the wave form of which FIGS. 3 and4 are representat1ve. The particular form, it will be understood, is determlned by the particular heart being studied and which may or may not contain abnormalities such as the diastolic murmur M of F IG. 4.

Turning now to a discussion of the right hand column of blocks in the diagramof FIG. 2, an electrical signal, similar to that used in electrocardiograplnc work, is picked up from a plurality of cutaneous electrodes 11 and ampiified in the amplifiers, a workable embodiment of which is shown in FIG. 10. As is well known in the electrocardlographic art, the electrodes 11 comprise an electrode 11a connected to the right arm of the patient, an electrode 11b connected to the left leg of the patient, and an electrode connected to the right leg of the patient. The right leg of the patient is then connected to the ground terminal of the system, and the electrodes connected to the right arm and the left leg of the patient are then capacitively coupled through capacitors 79 and 71 to the bases of the respective transistors 72 and 73 of the differential amplifier 17. The differential amplifier transistors 72 and 73 share a common emitter resistance 74 and have their base circuits forwardly biased at the same potentials by respective resistor chains 75 and 76. The collectors of these transistors are returned to a source of negative supply voltage through load resistances 79 and 80. As a consequence of this circuit, any potential difference which exists between the electrodes 11a and 11b is amplified and coupled for alternating current signals to the base of a first electrocardiogram amplifier 18, the coupling being accomplishedzthrough a capacitor 81 connected to the base of the transistor 82. The collector of this transistor is provided with a load resistance 83, and the emitter is returned to ground by another resistor 84.

to a source of 'to a diode 1%,

tive output pulses can be Forward bias is supplied to the base of the transistor 82 by a resistance chain comprising the resistors 85 and 86 and the base is bypassed to ground for high frequency by a srnall condenser 87. The bias level is set on the transister 82 so that its quiescent collector voltage is equal to one-half of the supply voltage. Since the emitter resistance 84 is not bypassed it serves to increase the input impedance of this amplifier stage. The negative feedback also provides more stable operation, and the higher input impedance tends to minimize the load on the differential amplifier i17.

The output of this amplifier stage 18 is taken through a capacitor 88 and applied to the base of an emitterfollower capacitor 89 having a grounded collector and having a load resistance 91 connected between its emitter and the source of positive supply voltage. This emitterfollower serves to present a high impedance to the first amplifier stage 18 and the lower driving impedance to the following amplifier stage 211, the emitter-follower being coupled thereto through a capacitor 91 connected with the base of the next amplifier transistor 5 2. Here again, this amplifier stage 20 is bypassed by a chain of resistors 93 and 94 so that its quiescent collector voltage is one-half of the supply voltage, the emitter of this transistor being returned to ground through a resistance 95 bypassed by a condenser 96, and the collector of the transistor 92 is coupled to a source of negative voltage by a load resistor 97. A capacitor 98 is connected between the collector and the base of the transistor 92 in order to provide substantial negative feedback at the higher frequencies, but very little feedback at the lower frequencies which are of principal interest in the intended application of this amplifier. The output of this, amplifier stage is then coupled by a capacitor 99 with a final emitterafollower stage 21 comprising a transistor ltltl having its collector coupled of the transistor is returned to ground by a load resistance 103, and the output from this stage is coupled through a capacitor 1194 to a switch 195 which is in turn coupled both sides of which are returned to groundby resistors 107 and 108 respectively. The output of the amplifier system shown in FIG. 10 is taken along the Wire 1% from the junction between the diode 106 and the resistance 1538.- The diode 1% is oriented so as topass only positive components of the output from the emitter-follower transistor 11%, and therefore the output of this amplifier comprises positive pulses. These posiseen in FIGS and are labeled positive pulses occur sound I.

P. it is to be noted that these li htly before dominant heartbeat Referring now to FIG. 1 1, showing a Working embodipositive supply voltage and having its base. forwardly biased by resistors 161 and MP2. I The emitter 'pacitor 125 and the input ofwhen triggered and is delivered through the diode 121 to the base of the transistor 111 to thereby cut oil this transistor. A switch 122 couples one of a plurality of capacitors 123, 124 to the lower end of the potentiometer 116, and the selected one of these capacitors together with the resistance in the voltage divider chain 114116 controls the time constant of the quasi-stable state of this multivibrator. It is to be understood that as herein used, the term monostable vibrator relates to a multivibrator with one stable and one quasi-stable state in which the same is' normally stable and is triggered to the quasi-stable state.

By varying the potentiometer 1.16 and by moving the switch i122 to select an appropriate capacitor 123, 124 it is possible to vany the time constant of this multivibrator 22 and thereby vary the length of the positive output pulse G (FIG; 5) obtained at the collector of the transistor 111.- llhis positive output pulse is then dilferentiated by a capacitor 125 and a resistor 126 so as to provide a positive spike at the beginning negative spike at the end of the same positive pulse. The diode 127 is coupled between the differentiating cathe next multivibrator stage 23 so as to pass only the negative spikes onto the multiviment of the delay multivibrator 22 and the gate control multivibrator 23, the delay multivibrator 22 comprises two transistors connected to provide monostable operation in which the transistor 11%) is conductive. The collectors of both transistors are connected to a source of positive voltage through respective load resistors 112 and 113, and the base of transistor 1 11 is normally biased on by a chain of resistors 114, and 116, the latter comprising a potentiometer. The base of the normally olf transistor 110 is coupled through resistances 1-17 and 1 18 to a voltage divider chain 119 and connected between ground and a source of negative potential, and in this manner the base of the transistor 111% ismaintained noncoductive when the transistor 111 is conductive. On the other hand, if the transistor 111 becomes nonconductive, the positive voltage at the collector electrode thereof increases and thereby biases the transistor 110 positively. The input lead 109 from the preceding emitter-follower circuit 21 is applied to the base of the transistor 116 as the delay time constant of differentiated by (FIG, 6), the

brator 23. p

The multivibrator 23 is also a monostable device in which the transistor 13!) is normally on and the transistor 131 is normally on. These transistors have their collectors coupled to the source of positive power by way of resistances 132 and 133 respectively, and the transistor also has its collector returned to ground by another resistor 134 which forms a voltage divider with transistor'132. The emitters of both transistors are directly returned to ground, and the base of transistor 131 is connected in a series voltage divider 135, 136 and 137, the latter resistor being a potentiometer. A series diode 138 is 'also conn'ected in this circuit so as to isolate the time constant formed by the capacitors 139 and 140 together with the resistances and 137 so as to prevent loading of these time constants by the base-emitter circuit of the transistor 131. The base of the other transistor 130 is also connected in a voltage divider compris ing the resistors 141,142, 143 connected between ground and the collector of the transistor 131, and negative bias is injected into this chain by way of a resistance 144 so as to insure that the transistor130 will normally remain cut off so long as the transistor 131 is conductive. This multivibrator operates in substantially the same manner multivibrator 22. The output pulse from the multivibrator 23 is delivered through a resistance 145 to a lead 146 which is also connected to one end of a capacitor 147, the other end of which is grounded for the purpose hereinafter stated. The lead 146 is then connected to the gate 24, FIG. 2, and serves to control which is normally conductive, this latter transistor is cut ofif and the time constant comprising one of the condensers 13 and the resistors 135 and 137 is charged up so that the transistor 130 is turned on for the duration of this time constant. Since during this quasi-stable state the transistor 131 is cut off, the collector thereof will be driven positive, and therefore a positive pulse will be delivered through the lead 146 for the duration of the the multivibrator 23. As stated above, thepositive pulse at the collector of transistor 111 is at the beginning of the pulse G and a of the same positive pulse.

a positive spike negative spike at the end Since it is the negative spike which triggers the multivibrator 23 and further since the positive pulse G at the collector of transistor 111 is coincidental with pulse P position of the leading edge of positive pulse G (FIG. 7) from multivibrator 23 is controlled by of the positive pulse G and a capacitor 125 and 126 so as to provide the time constant of multivibrator 22. As a result, it will be seen that the time constant adjusted by the potentiometer 116 and the switch 122 determinethe front edge of the pulse G from the multivibrator 23, and that the trailing edge of this pulse G from the multivibrator 23 is then adjusted by the appropriate selection of a capacitor 139 or 140 by changing the switch 143 to the appropriate position, and also by further adjustment of the potentiometer 137. In other words, after a range has been selected by appropriate adjustment of switches 122 and 148, fine adjustment of the leading and trailing edges of the gate pulse G, FIG. 7, is made by movement of the resistances 116 and 137. It is the pulse P from the wave form of FIG. 6 as delivered to a first multivibrator 22 by the amplifier circu't of FIG. 10 which controls the triggering of the first multivibrator circuit 22. Therefore, in the system shown in FIG. 2 the leading edge of the pulse G can be initiated at any time beginning with the occurrence of the small pulse P in FIG. 6, which small pulse represents the electrocardiogram impulse preceding the first of the dominant heartbeat sounds.

The gate according to the system of FIG. 2 is shown in FIG. 12, wherein two diodes 150 and 151 are coupled to a common point A which is in turn connected to the base of the transistor 153 comprising the emitter-follower 25 as illustrated in FIG. 2. The other end of the diode 150 is coupled to the lead 61 which is connected from the output of the sound amplifier circuit shown in FIG. 9. The other end of the diode 151 is connected through lead 146 to the output of the multivibrator circuit 23, FIG. 11, and both diodes are biased on one side at point A to an appropriate voltage by a resistance 152 which is connected to a source of positive potential. When the normally on transistor 1310f the multivibrator shown in FIG. 11 is conductive during the interval G in FIG. 5, it drives current through the resistance 133 and thereby lowers the voltage at the collector of the transistor 131 and also on the line 146. This voltage becomes less positive and therefore the diode 151 drives more current through the resistance 152 than would be the case if the collector of the transistor 131 stopped drawing current and the voltage at its collector went to the full plus 12 volts. In this latter case, the diode 151 would draw no current through the resistance 152 and therefore point A would become much more positive. By appropriate selection of the quiescent voltage appear.- ing at the line 61 which is the emitter of the transistor 55, the diode 150 can be selectively biased conductive, or nonconductive, depending on whether collector current is drawn through the transistor 131. As stated above, in the quiescent state, such current is normally drawn, and therefore the diode 150 is normally biased nonconductive. Thus, during the quasi-stable state of the multivibrator 23, a positive gate voltage G, FIG. 7, is applied to the diode 151 and the presence of this positive voltage permits the audio signals to pass through the gate from the lead 61 to the emitter follower 25. On the other hand, when the gate signal G is not present, during G intervals in FIG. 5, the diode 151 conducts current through the resistor 152 to a suflicient extent that the diode 150 becomes reverse-biased and therefore the gate is rendered nonconductive.

The resistor 145 and the capacitor 147 in FIG. 11 comprise an integration circuit which serves the purpose of rounding the leading andtrailing edges of the pulse G so as to prevent the introduction of switching transients thereby. In FIG. 11, a switch 149 is provided which, when opened, renders the collector circuit of the transistor 131 nonconductive, and thereby raises the positive voltage at the lead 146 to render the diode 151 nonconductive, and thereby render the diode 150 conductive. In other words, when the switch 149 is opened the gate is made continuously conductive and all of the sound signals from the amplifier illustrated in FIG. 9 pass through to the headphones 27. I I t turned to ground through a potentiometer The emitter-follower 25 has its collector returned to the source of positive potential and has its emitter re- 154 which is bypassed by a small condenser 155 which serves to eliminate high frequency components of the signal passing through the amplifier 153. emitter-follower 25 is delivered through a capacitor 156, and the amplitude of the signal therethrough is adjustable by adjustment of the potentiometer 154.

The audio signal is fed from the capacitor 156 to the base of the transistor 157 which comprises the final amplifier 26, the base being forwardly biased by a voltage divider chain comprising the resistors 158 and 159. This final amplifier 26 is biased to allow a dynamic negative swing of approximately 10 volts in amplitude without saturation. The resistor 169, connected in series with the base of the transistor 157, tends to limit the driving signal and thereby minimize saturation tendencies. Collector to base feedback through resistor 161 and capaci tor 162, and the use of an unbypassed resistor 163 in the emitter circuit provide degenerative feedback and stabilize the operating point of this amplifier. Only part of the emitter circuit is unbypassed, the resistor 164 being bypassed by a condenser 165. The amplifier transistor 157 is provided with a load resistor 166 which is coupled to the source of positive potential, and the output signal to the earphones 27, or other output transducer, is provided through a coupling capacitor 167.

In the system of FIG. 1, the gate control 5 comprises a delay multivibrator as is illustrated in FIG. 14. In this latter figure, the output of the amplifier system of FIG. 9 is connected thereto as at 61 and leads to a potentiometer 170. The multivibrator 5 comprises two transistors 171 and 172 connected to provide monostable operation in which transistor 171 is normally 011 and transistor 172 is normally on. The collectors of both transistors are connected to a source of positive voltage through respective load resistors 173 and 174, the base of transistor 172 is normally biased by a chain of resistors 175, 176 and 177, of which 176 is a potentiometer. The base of transistor 171 is coupled through resistance 178 and the resistance of potentiometer to a voltage divider chain comprises resistors 179 and 181) connected between ground and a source of negative voltage as shown. In this fashion, the base of transistor 171 is maintained nonconductive when transistor 172 is conductive. On the other hand, if transistor 172 becomes nonconductive, the positive voltage at the collector electrode thereof increases and thereby biases the transistor 171 positively.

Every time a positive pulse I (FIG. 3) is applied to the base of transistor 171 through lead 61 to the potentiometer 170, the transistor 171 is driven positive. The negative pulse generated at the collector of transistor 171 is delivered through diode 181 to the base of transistor 172 to thereby cut off this transistor. Switch 182 selectively couples one of the capacitors 183, 184 to the resistance of potentiometer 176 and the selected one of these capacitors together with resistors and 176 determine the time constant of the quasi-stable state of transistor 172.

FIG. 13 illustrates the circuit of the inhibitor gate 6 of FIG. 1 as well as the amplifier 7 of that same figure. In the gate 6, the base of transistor 189 is negatively biased by resistors 190 and 191 connected to the voltage divider chain comprising resistors 192 and 193 while its collector is connected to a source of positive voltage by load resistor 194. The gate 6 is coupled to the gate control 5 (FIG. 14) by the capacitor 195 through conductor 188. The collector of transistor 189 is connected to emitter-follower 22 by conductor 61 and thus receives the amplified heartbeat sound signals therefrom. Thus, the heartbeat signal is always present at the collector of transistor 189 and due to the negative bias on the base of transistor 189, this signal will continue unimpeded to capacitor 196 and potentiometer 197. However, when The output from the the positive going wave form from the gate control multivibrator appears at 188, transistor 189 becomes heavily forward biased which causes the collector to emitter impedance to become very low, shortening the heartbeat Relatingback to FIGS. 3-8 and describing operation of the device in conjunction with the form of theinvention shown in FIG. 2, the sound signals of the heart are as shown in FIGS. 3 and 4, the latter figure showing the presence of a murmur M. FIG. 5 illustrates the pulse G which is generated by the multivibrator 22 as triggered by the pulse P, FIG. 6, which is the electrical impulse preceding the dominant I sound of FIGS. 3 and 4. Thus, the pulse P is presentat the multivibrator 22 through the conductor 109 (FIG. 11) and this triggering pulse P for the multivibrator 22 causes the pulse G to be present at the capacitor 125, the duration of the pulse G being dictated by the time constant involved inconjunction with the multivibrator 22 as aforesaid and which may be varied if desired. The capacitor 125 and resistance 126 differentiate the pulse G to produce a positive spike at the leading edge of the pulse G and a negative spike at the trailing edge of the pulse G. Due to the orientation of the diode 127, it is the negative spike at the trailing edge of the pulse G which triggers the gate multivibrator 23 whose output is depicted in FIG. 7 of the drawings. Thus, the leading edge of pulse G of the multivibrator 23 is coincidental with the trailing edge of the pulse G of the delay multivibrator 22. The duration of pulse G is determined by the time constant of the multivibrator 23 as aforesaid and may be varied if desired.

The gate 24 of FIG. 12 receives both the signal from the microphone through conductor 61 and the signal from the gate multivibrator 23 through the conductor I46 and such gate 24 is operative to pass the heartbeat sound signals only at such time as the pulse G of FIG. 7 is present. Thus, in the specific example shown in FIGS. 4-8, only the murmur M will be passed onto the emitter follower 25 and ultimately to the sound reproduoer means 27 in FIG. 12' Thus, the gate control in accordance with the invention as shown in FIG. 2 includes a delay multivibrator triggered by pulse P'of FIG. 6 and generating a pulse whose duration is controlled or predetermined to produce the pulse G of FIG. 5 and such control means also includes the gate control multivibrator 23 which generates a pulse G of predetermined duration which is triggered in response to the trailing edge of pulse G to so control the gate 24 as to pass the heartbeat sounds only at such times as the pulse G is present.

In contrast to the above, the operation of the invention according to FIG. 1 embodies a more simplified gate and gate control means in accordance respectively with FIGS. 14 and 13 of the drawings. The gate control 5 in FIG. 14 receivessignals through the conductor 61 directly from the sound pickup means and in accord ance with the circuitry involved, including the. threshold potentiometer 176, the output of the gate control 5, through conductor 138 is a pulse of predetermined and preferably variable duration which is initiated by the dominant I heartbeat sound. This pulse is passed onto shown in the drawings, it will be appreciated that it will be of form similar vto However, as previousl is triggered by pulse tool 5 is triggered b Thus, successive out separated by an interval period of sound between su beats. Thus, gate 6 dilTe-rs b the latter is normally noncon ductive by igate control 22 mally conductive and is re control 5.

To illustrate one specific embodiment vention according to FIGS. 2 and 9-12,

whos

l0 that shownin FIG. 5 (pulse G y mentioned, unlike pulse G whi P of FIG. 6, the output of gate cony the dominant I heartbeat sounds. pulses of gate control 5 will be e duration detenmines each ccessive dominant I heartasically from gate 2 4- in that ductive and is rendered con- -23, whereas gate '6 is norndered nonconduotive by gate ouit values apply to the latter figures.

FIGURE 9 57-1OOK FIGURE 10 FIGURE 11 of the present. inthe following cir- While a preferred embodiment of the invention has been shown, the inventive principles involved are capable of assuming other physical embodiments without departing from the spirit of the invention and the scope or the appended claims.

What is claimed is: V

1. An electronic stethoscope system responsive to body sounds and electrical impulses, comprising a microphone for picking up body sounds, sound signal amplifier means connected with the microphone and delivering electrical signals proportional thereto, sound reproducing means, signal gate means coupling said amplifier means to said reproducing means, said Iga-te means selectively controlling the pass-age' of said signals therethrough, elect-rode means tor picking up body impulses, impulse amplifier means coupled with said electrode means and delivering amplified electric impulses proportional to said body impulses, and gate control means coupled to said gate means for controlling the conductivity thereof and coupled to said impulse amplifier means and actuated by amplified electric impulses to change the conductivity of the gate means, said gate control means comprising a monostable delay multivibnator coupled to be [triggered by said impulses and having a first R-C time constant determining the duration of its output Wave when triggered to its quasi-stable state, a monostable gate-voltage multivibrator raving a second R-C time constant determining the dui at-ion of its output gate-voltage wave when triggered to its quasi-stable state, and coupling means connecting the gate-voltage multivibrator to the delay multivi-brator to be triggered by the trailing edge of its quasi-stable output Wave. 1 2. In a system as set forth in claim ,1, said coupling meansco nprising a difierentiating circuit differentiating theouasi-stable output wave of the delay multivibrator, and diode means poled to pass the differentiated signal [from the trailing edge of said wave, but to block the differentiated signal from the leading edge of said Wave. 3. In a system as set forth in claim 1, R-C time constant adjusting means for adjusting the duration of the gate voltage applied to the gate means when the gatevoltage multivibrator is in quasi-stable state.

References Cited in the file of this patent UNITED STATES PATENTS 2,577,827 Tompkins Dec. 11, 1951 2,827,040 Gilford Mar. 18, 1958 2,865,365 Newland et al. Dec. 23, 1958 Richards 3,03 0,946 Apr. 24, 1962 

1. AN ELECTRONIC STETHOSCOPE SYSTEM RESPONSIVE TO BODY SOUNDS AND ELECTRICAL IMPULSES, COMPRISING A MICROPHONE FOR PICKING UP BODY SOUNDS, SOUND SIGNAL AMPLIFIER MEANS CONNECTED WITH THE MICROPHONE AND DELIVERING ELECTRICAL SIGNALS PROPORTIONAL THERETO, SOUND REPRODUCING MEANS, SIGNAL GATE MEANS COUPLING SAID AMPLIFIER MEANS TO SAID REPRODUCING MEANS, SAID GATE MEANS SELECTIVELY CONTROLLING THE PASSAGE OF SAID SIGNALS THERETHROUGH, ELECTRODE MEANS FOR PICKING UP BODY IMPULSES, IMPULSE AMPLIFIER MEANS COUPLED WITH SAID ELECTRODE MEANS AND DELIVERING AMPLIFIED ELECTRIC IMPULSES PROPORTIONAL TO SAID BODY IMPULSES, AND GATE CONTROL MEANS COUPLED TO SAID GATE MEANS FOR CONTROLLING THE CONDUCTIVITY THEREOF AND COUPLED TO SAID IMPULSE AMPLIFIER MEANS AND ACTUATED BY AMPLIFIED ELECTRIC IMPULSES TO CHANGE THE CONDUCTIVITY OF THE GATE MEANS, SAID GATE CONTROL MEANS COMPRISING A MONOSTABLE DELAY MULTIVIBRATOR COUPLED TO BE TRIGGERED BY SAID IMPULSES AND HAVING A FIRST R-C TIME CONSTANT DETERMINING THE DURATION OF ITS OUTPUT WAVE WHEN TRIGGERED TO ITS QUASI-STABLE STATE, A MONOSTABLE GATE-VOLTAGE MULTIVIBRA- 